The Global Forecast System (GFS) chart continues to roll out the usual 4 updates per day, these updates have been showing large changes in the long-range forecast, but one fact now beginning to become reliable is cold air is set to flood in, for the start of the Christmas week. The GFS 12z run on 5th December is showing a large barrage of cold air moving in from the north-west, which would bring snow to northern regions, with wintry showers elsewhere. The 06z run is showing a slightly milder start to the week, but has a greater risk of cold air under cutting the warm air from the east.
The 12z run also suggests an area of cold air moving across the United Kingdom during the weekend being 19th and 20th December. This does bring the risk of snow to Scotland, Northern Ireland, Northern England and Wales. Wintry showers would be unlikely elsewhere across the United Kingdom, but we are still 15 days away from this even, so anything can change.
The snow risk for Christmas day has remained unchanged for the past 5 days, but as we begin to approach the 7 day window, we will see the changes alter significantly day by day.